1. Field of the Invention
The present invention relates to an optical distance sensor that applies a light beam emitted from a light emitting element placed at a reference point to an object, detects a light beam reflected by the object at a distance to be measured by using a light detecting element, and measures the distance from the reference point to the object, or a location or displacement of the object using a triangulation technique.
2. Description of the Prior Art
FIG. 19 is a perspective view showing a prior art optical distance sensor that measures a distance to an object, or a location or the like of the object using a triangulation technique as disclosed in international patent application No. PCT/JP98/04144. In FIG. 19, reference numeral 101 denotes an input optical fiber, reference numeral 102a and 102b denote output optical fibers, reference numeral 103 denotes a three-layer waveguide in which a core layer 103a having a high refractive index is sandwiched by a cladding layer 103b having a low refractive index, reference numerals 104a and 104b denote plane mirrors on side walls of the three-layer waveguide 103, each plane mirror being covered with a reflection coating, reference numerals 105a and 105b denote curved minors on side walls of the three-layer waveguide 103, each curved mirror being covered with a reflection coating, reference numeral 106a and 106b denotes end faces of the three-layer waveguide 103, reference numerals 107a and 107b denote cylindrical lenses, reference numeral 108a denotes a light beam emerging from the cylindrical lens 107a, reference numeral 108b denotes a light beam that is reflected by an object to be measured (not shown in the figure) and is incident upon the other cylindrical lens 107b, and reference numeral 109 denotes a Y-branch waveguide.
In operation, a light beam used for detection is introduced into the three-layer waveguide 103 by way of the input optical fiber 101. The incident light beam is confined in the direction of the thickness of the three-layer waveguide and is brought to a focus at a predetermined position in a parallel direction parallel to a substrate by the curved mirror 105a after it is reflected by the plane mirror 104a. The light, which has been reflected by the curved mirror 105a, emerges from the edge surface 106a and is then incident upon the cylindrical lens 107a. The light beam is brought to a focus at a predetermined position while its optical axis is deflected by the cylindrical lens 107a. This light beam is then reflected by an object (not shown in the figure) placed forward of the outgoing light beam from the cylindrical lens 107a, and is incident upon the other cylindrical lens 107b and is introduced, by way of the edge surface 106b, into the three-layer waveguide 103 again. The introduced light beam is confined in the direction of the thickness of the three-layer waveguide and is reflected by the plane mirror 104b while it is converged in the parallel direction to a surface of the substrate by the curved mirror 105b, so that the light beam comes into a focus at a branching point of the Y-branch waveguide 109. The light beam at the branching point is introduced into both the output optical fibers 102a and 102b after it is separated into two parts with a light power ratio corresponding to a position where the light beam is focused to the branching point of the Y-branch waveguide 109. The two separated light lays are therefore output to outside the optical distance sensor.
The position of a light spot that is imaged at the branch point of the Y-branch waveguide 109 changes according to the location of the object to be measured by using a triangulation technique. In other words, the ratio between the powers of the two light beams respectively introduced into the output optical fibers 102a and 102b changes according to the location of the object to be measured. By measuring this change by using two photo detectors (not shown in the figure) respectively connected to the two output optical fibers 102a and 102b, the location of the object to be measured can be determined.
Japanese patent application publication (TOKKAIHEI) No. 3-102727 discloses an optoelectronic switch intended for factory automation, in which a lens block having a lenticular entrance surface and a lenticular exit surface coupled to each other via a prism is arranged on a substrate on which a light emitting element, a position detector, and a signal processing unit are mounted, the optoelectronic switch applying a light beam to an object to be detected which is placed in a detection area and detecting light reflected by the object to detect the presence of the object.
A problem with the prior art optical distance sensor constructed as above is that when the waveguide having a function of converging light beams in a direction parallel to a substrate is formed, since the core layer 103a and the two cladding layers 103b are laminated alternately so that the core layer is sandwiched between the two cladding layers, it is impossible to form the optical distance sensor in one process and therefore the manufacturing cost increases. Another problem is that since optical fibers are used for optical I/O, the handleability is bad. In addition, since the cylindrical lenses 107a and 107b are coupled to the thee-layer waveguide 103, the cost of assembling the optical distance sensor increases. Coupling loss occurs because air or a bonding adhesive enters a gap between each of the cylindrical lenses 107a and 107b and the three-layer waveguide 103. Additionally, since a reflection coating is adhered to the surface of each of the plane mirrors 104a and 104b and the curved mirrors 105a and 105b, light is absorbed by the reflection coating and performances, such as a signal to noise ratio, are deteriorated. In addition, to unite downsizing and high precision measurement, it is necessary to lengthen the optical path length in the sensor so as to enlarge the magnification of image formation of the optical system. So, since the direction in which the object to be measured can be moved, i.e., the measurement direction along which measurements are carried out is parallel to the substrate, as in the case of the optoelectronic switch disclosed in Japanese patent application publication No. 3-102727, there is no alternative but to lengthen the optical path length of the optical distance sensor in the measurement direction. As a result, it is impossible to make the optical distance sensor compact with respect to the measurement direction. In addition, since the diameter of the cylindrical lenses cannot be enlarged according to a size limitation, the prior art optical distance sensor cannot make long-distance measurements.
The present invention is proposed to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a small-size, low-cost, and easy-to-handle optical distance sensor.
In accordance with the present invention, there is provide an optical distance sensor that applies a light beam emitted out of a light emitting element placed at a reference point to an object to be measured, detects a light beam reflected by the object to be measured by using a light receiving element, and measures a distance from the reference point to the object to be measured, or the location or displacement of the object to be measured by using a triangulation technique, the sensor including: a substrate on which the light emitting element and the light receiving element are disposed; and an optical structure body in which a first converging mechanism for converging the light beam emitted out of the light emitting element, a second converging mechanism for converging the light beam reflected by the object to be measured, and a reflecting mechanism for deflecting the light beam reflected by the object to be measured twice are formed in one piece.
Consequently, in accordance with the present invention, since the light emitting element and the position sensitive light receiving element are arranged on the same substrate, the assembling cost can be reduced and the accuracy of the relative position between the light emitting element and the position sensitive light receiving element can be improved. Furthermore, since the optical structure body provided with the first and second converging mechanisms and the reflecting mechanism can be formed in one piece with a transparent resin, the manufacturing cost can be reduced, the cost of assembling the first and second converging mechanisms and the reflecting mechanism can be eliminated, the optical distance sensor can be downsized, and the accuracy of the relative position among those components can be improved. In addition, since the optical structure body has no inclusion with a different refractive index such as air and an adhesive, coupling loss due to a difference in refractive indexes can be eliminated. Furthermore, since the optical axis of light emitted out of the light emitting element and the optical axis of light reflected by the object to be measured can be deflected by the reflecting mechanism, the optical path length in the optical structure body can be lengthened, and therefore the magnification of image formation of the optical distance sensor can be maintained high and the displacement of the object can be detected with a high degree of accuracy even if the optical distance sensor is downsized. In addition, since the optical axis of light reflected by the object to be measured is deflected twice by the reflecting mechanism and the measurement direction along which measurements are carried out is perpendicular to the substrate, the thickness of the optical distance sensor can be reduced with respect to the direction in which the object to be measured can be moved.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.